1. Field of the Invention
The present invention relates to a wavelength division multiplexing optical device and a manufacturing method therefor.
2. Description of the Related Art
The widespread use of a communication network using optical fiber transmission is indispensable to construct a multimedia information society. It is therefore necessary to realize a photodetection module capable of efficiently converting an optical signal into an electrical signal at a low cost. Further, wavelength division multiplexing optical communication for multiplexing light having different wavelengths by utilizing wavelength independence of light to transmit the resultant wavelength division multiplexed light is expected to provide various services including bidirectional communication and service multiplexing. It is therefore essential to use a wavelength division multiplexing optical device for multiplexing optical signals having different wavelengths and/or demultiplexing wavelength division multiplexed signal light.
A conventional waveguide type wavelength division multiplexing optical device is described in Japanese Patent Laid-open No. 63-33707. In this conventional device, an optical waveguide having a Y branch portion is formed on a silicon substrate, and a groove is formed so as to extend across the Y branch portion. A dielectric multilayer film filter is inserted in this groove. This type wavelength division multiplexing optical device has a small size and good isolation characteristics, so that it is advantageous over a Mach-Zehnder type wavelength division multiplexing optical device and a fiber fusion splice type optical device.
However, the above-mentioned wavelength division multiplexing optical device structure has a problem that insertion of the filter into the groove is difficult. That is, the filter film having a thickness of about 15 .mu.m must be inserted into the groove having a width of about 25 .mu.m, thus making the insertion difficult. Further, to suppress an increase in insertion loss, an error of tilt angle of the filter from a vertical direction must be suppressed within about 0.5.degree.. Accordingly, it is difficult to stably fabricate a wavelength division multiplexing optical device in the conventional structure.